A Trump hat sits on a table outside of the rally for Republican U.S. presidential nominee Donald Trump in New York City in November, 2016.
Photograph: Andrew Kelly/Reuters

In 2016, as Donald Trump was busy securing the Republican nomination by promising to “Make America Great Again”, a survey of Americans asked a seemingly simple question: in which year was the country great in the first place? Unfortunately, the results were not so straightforward and instead of a consensus, respondents’ choices were spread out across the last 70 years. But an analysis by the Atlantic found one factor that seemed to influence people’s responses: their age. The younger a participant was, the more recent the year they tended to choose.

This correlation was fairly weak, and it would be easy to dismiss it as a fluke. Yet recent research published in the Journal of Applied Research in Memory and Cognition has found that age is important. In this study, Americans disproportionately chose the years of their own youth as the country’s greatest years – no matter how old they were now. This finding is the latest involving a phenomenon known as the reminiscence bump.

The reminiscence bump

One of the most robust findings in memory research is that people recall more memories from young adulthood compared to other periods of their life. For example, if you ask a group of people to list important events from their lives, you see a bump corresponding to a greater number of memories for events that occurred between the ages of 10 and 30.

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Researchers have found this reminiscence bump in a number of different memory experiments. For instance when people are asked to provide a memory in response to a cue word, or when they report the years they encountered their favourite books and movies, they disproportionately recount memories from young adulthood.

And it doesn’t just occur for personal memories. When people list important public events – deaths of well-known people, sporting events, terrorist attacks and so on – they also show a reminiscence bump. Interestingly, people even predict that the most important public events will occur when a fictional person is between 11 and 30 years old, even though someone’s age should not have any effect on these kinds of events.

America’s greatest year

Intuitively, it seems like a person’s age should also be independent of their country’s greatness, over which they presumably have very little personal control. But Professor Maryanne Garry, a memory researcher at the University of Waikato who is well-versed in the reminiscence bump, thought otherwise. Every time Trump said that he was going to “Make America Great Again”, Garry says she suspected that he was “taking Americans to a place that would be different for every one of them”.

In the recent study, Garry’s team first asked a group of 100 Americans to list the key events that they consider to have shaped the country’s identity. From this data they produced a “top ten” list of the most commonly reported events, for example the signing of the Declaration of Independence and the Second World War.

The researchers then asked a separate group of 496 people which year they would describe as America’s greatest, and why they chose that particular year. Less than 40% of people chose a year related to one of the top ten events from the previous study - for example, 1776 because it was the year the Declaration of Independence was signed.

The interesting findings came from the remaining participants who did not pick a “top ten” year. When the researchers examined how old these people were in the year they chose, they found that the majority picked a year from their youth, with 60% selecting a date between their birth and their 20th birthday. In comparison, relatively few chose a year in the 100 years leading up to their birth, or after they were 30 years old.

The same pattern of responses was then also found in a second group. And importantly, participants ranged in age from 19 to 84, so each person’s period of youth corresponded to a different era in American history.

In other words, people’s choice of great year produced a distribution that looked very much like a reminiscence bump.

Why do we have a reminiscence bump?

Many researchers believe that the reminiscence bump reflects the strategies we use to retrieve key memories from our life. As Garry puts it: “I have a vast soup of experiences in my life - how do I wade through to try and find the most important ones?”

One theory is that that our culture provides a sort of blueprint that we use to determine which memories are important. We will tend to better recall experiences that are culturally-valued, and a lot of those events occur when we are children and young adults. This is the period when we graduate from school or university, work in our first jobs, and have our first romantic partners.

A slightly different idea suggests that we have more autobiographical memories from our youth because it is when we are forming our identity, and we tend to access memories from this period more because they define who we are as adults. Similarly, we have more memories for public events from our younger days because this is also when we are forming a generational identity.

This most recent study doesn’t clearly favour any particular theory. But it does have something to say about political rhetoric. Although a large group of people named America’s greatest year at a point in their youth, for some this meant the 1950s, for others the 2010s – quite different decades of American history.

Garry suggests that this could be where slogans like “Make America Great Again” get their power. For each of us, they invoke a time in our own lives where we had our first love, saw our favourite movies, experienced key life events. “They’re really effective messages”, she says. “We think we are on the same page, but we are actually on separate pages.”